The present invention relates to briquetting machines and, in particular, to briquetting rolls and removable segments therefore.
Briquetting machines are known devices which generally comprise a pair of wheel-like rolls geared together to cooperatively turn in opposing directions on parallel axes with the peripheral surfaces of each respective roll positioned in linear axial alignment with one another so that material introduced to the rolls is captured by the molding surfaces of the rolls and compressed into briquets by passage through the adjoining molding surfaces.
Briquetting apparatus and techniques have been used to compact and/or mold materials at both low temperatures and pressures as well as high temperatures and pressures for materials such as charcoal, iron ore, metal chips, etc. Generally, high pressure briquetting at elevated temperatures places additional demands upon the commonly employed rotary molds. In particular, rotary mold segments are subject to cracks from stress and to wear due to rocking and abrasion of the mold surface by the material to be molded.
It has been recognized that briquetting roll designs incorporating replaceable mold segments should permit easy removal and replacement of worn or broken segments with as little down time as possible. Also, inexpensive fabrication of durable segments which may be firmly secured in proper alignment are long known goals of segment design. The use of rolls comprised in part of a plurality of replaceable mold segments having surface cavities capable of receiving material to be briquetted is described in many prior art patents including U.S. Pat. Nos. 3,907,485; 4,306,846; and 4,097,215.
U.S. Pat. No. 3,907,485 describes replaceable mold segments adapted for placement upon the periphery of a cylindrical central member. These mold segments are affixed to the cylindrical central member by fasteners engaging projections extending outwardly from the side walls of the mold segment. This configuration of the mold segment cooperates with the central member such that radial compression forces applied to the mold segment are transmitted through the bottom surface of the mold segment, which bottom surface is coplanar with the projections from the side walls. The application of such forces to the mold segments produces bending stresses in the mold segment that can result in premature failure due to cracking of the strong part brittle mold segment.
U.S. Pat. No. 4,306,846 describes the use of a symmetrically shaped replaceable mold segment for a briquetting roll. These segments have side walls including upper and lower portions, the upper portions of which are disposed at an angle convergent with respect to a top working surface, and the lower portions of said side walls are divergent with respect to the axis of rotation of the rolls.
U.S. Pat. No. 4,097,215 describes a briquetting press roll which comprises a cylindrical core having a regular polygonal cross-section and a plurality of equal planar sections around its peripheral surface to which are attached a plurality of removable mold segments each having a flat bottom surface with said segments being attached by retaining rings.
Thus, prior art processes, techniques, and apparatus have been employed with varying degrees of success to alleviate the foregoing problems relating to premature failure or wear of roll segments. Some prior art devices go to great lengths to overcome these wear and cracking problems. For example, U.S. Pat. No. 2,958,902 describes the use of exchangeable segments which when attached to a briquetting roll are aligned so that the separation gap between segments forms an acute angle with cylinder generatrices which are parallel to the roller axis. The foregoing arrangement purportedly reduces wear by reduction of non-uniform forces due to overlapping separation gaps (Col. 1, lines 25-67). This device has the disadvantage of high machining costs due to it complicated design as best illustrated FIGS. 2, 3, 11 and 14.
As mentioned above, prior art segments suffer from wear due to rocking of the segment in its seat. This movement of a segment with respect to its seat occurs as a force travels across the arcuate molding surface of the segment causing the segment to pivot due to aberrations in surface contact. Since this rocking movement causes undesirable wear, attempts are made to minimize rocking in order to prolong segment life. One way to minimize rocking is to reduce the surface aberrations which act as "pivot points" for rocking. Machining of contact surfaces between segment and core seat will reduce rocking. Advantageously, the present invention reduces machining time and costs by allowing machining of flat surfaces which include at least one right angle between two flat planar surfaces. Use of a right angle allows utilization of uncomplicated fixtures in the machining process. Simplification of machining is especially desired to lower the time and cost of such operations in those countries having high labor costs.